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Tar and pitch of themselves are too soft for these in-tentions ; even the pitch being liable to be melted off bythe heat of the fun in summer, however firm in the coldof winter. Different powdery substances, as ashes, ochresand other mineral pigments, have been mixed with them,but without remedying the imperfection so effectually ascould be wished. In the Swediffi transactions for theyears 1742 and 1740, two compositions are recommended,which are said to be firm, durable, and glossy.

One is prepared by melting the tar over a moderatefire, so as to make it fluid but not to boil, and stirring inas much coal dust as will render it thick: this mixture,the author fays, is to be laid on with wooden trowels, ina hot day, as thick or as thin as shall be thought proper.The other is prepared by mixing the melted tar with asufficient quantity of lamp-black : a little of this mixtureis spread upon the upper side of each tile with a stiff,short-haired, painting brush : next day, when dry, thetiles are done over with tar alone, and two days after withtar again : this coating being well dried, which in sum-mer, according to the author, is generally in eight or tendays, some powdered lead ore is strewed over it, and wellrubbed in, first with a coarse and afterwards with a finelinen cloth ; from this it receives a sparkling appearance.

I tried both these compositions, and found them of agood black colour: when the bodies coated with themare held before the fire till the surface begins to run, theybecome glossy. They are not however wholly exemptfrom the inconveniencies complained of in the others.For though the tar was made as thick, both with thecoal dust and lamp-black, as was consistent with its beingspread smooth even in a hot sun and while warm fromthe fire, it afterwards softened in the fun considerably;

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